Evolution Of Surface Morphology Research Articles

Morphology evolution of the aluminum surface in a fluorine-containing environment.

The interaction between aluminum (Al) and F and O atoms is essential to understand the etching process of Al and alumina (Al2O3) by fluorine-containing gases. In addition, it also has an influence on the corrosion behavior of Al devices, e.g., the Al collector in lithium-ion batteries operates in fluorine-containing electrolytes. However, the understanding of the structural evolution of the Al surface by fluorination at the atomistic level still remains elusive. Here, the thermodynamic and kinetic behaviors of F adatoms as well as co-adsorbed F and O adatoms on typical Al surfaces have been systematically investigated by combining density functional theory (DFT) calculations, canonical Monte Carlo (CMC) simulations and reactive molecular dynamics (RMD) simulations. The results of DFT calculations indicate that there is a repulsion (about 0.07 eV on Al(111) and Al(110), and 0.7 eV on Al(100)) between the first nearest neighboring (1NN) F adatoms, while an attraction of 0.14 eV on Al(111) exists within a 1NN F-O pair. CMC simulations reveal that the configurations of co-adsorbed F and O adatoms on the Al(111) surface at medium to low temperature (<600 K) and low total coverage (<0.2 monolayer, ML) have F adatoms dispersed in the hexagonal islands of O adatoms due to the attraction within the O-O and F-O pairs and the repulsion between F adatoms. As the coverage increases, the surface undergoes serious deformation. The average 1NN coordination numbers (1st CN) of O-to-O, F-to-O and F-to-F are six, three and zero, respectively. As the temperature increases, the interactions among adsorbates begin to be disrupted: the 1st CNs of O-to-O and F-to-O decrease, while that of F-to-F increases. The O-F hexagonal pattern remains until above the Al melting temperature (>1200 K). For F adatoms, both their migration on the surface and the penetration into the subsurface are easier than those of O adatoms, confirmed by both the DFT and RMD simulations. Our study on the co-adsorbates with opposite lateral interactions is instructive for understanding the thermal etching of Al and Al2O3 by fluorine-containing compounds.

Surface morphology evolution and tribological behavior in nanosecond pulsed laser polishing of S136 mold steel

Laser polishing (LP) is anticipated to become a new generation of surface polishing technology for the industrial field due to its high efficiency, reliability, and environmental friendliness, while few studies have reported the effect of LP on tribological behavior. Herein, the surface morphology, surface roughness, phase composition, surface hardness, and tribological behavior of S136 mold steel after nanosecond pulsed LP were investigated. The results of the orthogonal experiment suggested that the effect on surface roughness was in the following order: laser fluence > scanning speed > overlap factor along Y direction. A smooth and defect-free surface with a surface roughness Sa of 80 nm and a surface roughness reduction rate of 55.8% was achieved using the optimal LP parameters, and the LP mechanism was identified as the shallow surface melting. The wear tests indicated that LP weakened the wear resistance of S136 mold steel, which was attributed to the appearance of the γ-Fe phase on polished surface resulting in an 8% decrease in surface hardness, but this phenomenon is tolerable and controllable. Moreover, a combined action of abrasive wear and adhesive wear was confirmed on the LP specimens, whereas the abrasive wear was determined on the original specimen.

Laser surface treatment to enhance the adhesive bonding between steel and CFRP: Effect of laser spot overlapping and pulse fluence

Adhesive bonding is widely applied in joining between steel and carbon fiber reinforced plastics (CFRP), while the surface characteristics of steel have a significant effect on the joint strength. To improve the adhesive bonding between DP590 steel and CFRP, surface modifications of steel by laser surface treatment with different overlap rate of laser spot and pulse fluence were applied and investigated. The evolution of surface morphology, contact angle, surface energy, and surface chemical composition of DP590 steel after laser treatment with different parameters were also studied. The results showed that surface roughness, surface energy and polar component of surface energy after treatments were closely related to the interfacial bonding strength between steel and adhesives. Specifically, higher pulse fluence can increase the surface roughness of the steel, which reduced the contact angle and improve the surface energy, thus not only leading to a better mechanical interlocking effect, but also improving the surface wettability of the adhesive to the steel surface. When there was 50 % overlapping of the laser spots, the surface wettability was further improved. In addition, the strengths of steel-CFRP joints obtained with both epoxy adhesive E-120HP and polyurethane adhesive PU6700 were significantly enhanced by laser surface treatment. Especially for the joints bonded with E-120HP, which is a high-strength and poor-toughness adhesive, the shear strength can be increased by 299 %, from 4.10 ± 0.17 MPa to 16.35 ± 0.89 MPa after laser treatment. More importantly, the adhesive failure along steel-adhesive interface was entirely avoided. This study provides both technical and theoretical guidance of laser surface treatment for fabricating high-performance metal-polymer hybrid structures by adhesive bonding.

Investigation of Material Removal Distributions and Surface Morphology Evolution in Non-Contact Ultrasonic Abrasive Machining (NUAM) of BK7 Optical Glasses.

A non-contact ultrasonic abrasive machining approach provides a potential solution to overcome the challenges of machining efficiency in the high-precision polishing of optical components. Accurately modeling the material removal distribution (removal function (RF)) and surface morphology is very important in establishing this new computer-controlled deterministic polishing technique. However, it is a challenging task due to the absence of an in-depth understanding of the evolution mechanism of the material removal distribution and the knowledge of the evolution law of the microscopic surface morphology under the complex action of ultrasonic polishing while submerged in liquid. In this study, the formation of the RF and the surface morphology were modeled by investigating the cavitation density distribution and conducting experiments. The research results showed that the material removal caused by cavitation bubble explosions was uniformly distributed across the entire working surface and had a 0.25 mm edge influence range. The flow scour removal was mainly concentrated in the high-velocity flow zone around the machining area. The roughness of the machined surface increased linearly with an increase in the amplitude and gap. Increasing the particle concentration significantly improved the material removal rate, and the generated surface exhibited better removal uniformity and lower surface roughness.

Surface morphology evolution of C-plane sapphire during multi-step thermal annealing

The surface morphology evolution of the C-plane (0001) sapphire surface with the 4° miscut angle towards A-plane is thermally annealed at temperatures of 1100 °C and 1200 °C for different dwell times varying between 3-12 hours in multiple steps, resulting in a total of 30 hours. Atomic Force Microscopy (AFM) observations are used to systematically study the effects of the thermal annealing process, temperature, and time on the evolution of the periodicity and step height of structures. The step-terrace structures with straight step-edges along the direction were observed over the entire surface after 3 hours of annealing at 1100 °C. The step-terrace structure morphology evolves through the step-bunching and facet coarsening mechanisms during the multi-step thermal annealing process. Step-bunching begins with the formation of contact points between the adjacent steps by diffusion of atoms. Its onset is associated with a threshold value of the periodicity of step-terrace structures. By varying the annealing temperature during the multi-step thermal annealing process, the evolution of step-terrace structures can be manipulated by delaying the process of step-bunching.

Modeling tungsten response under helium plasma irradiation: a review

Tungsten, a leading candidate for plasma-facing materials (PFM) in future fusion devices, will be exposed to high-flux low-energy helium plasma under the anticipated fusion operation conditions. In the past two decades, experiments have revealed that exposure to helium plasma strongly modifies the surface morphology and hence the sputtering, thermal and other properties of tungsten, posing a serious danger to the performance and lifetime of tungsten and the steady-state operation of plasma. In this article, we provide a review of modeling and simulation efforts on the long-term evolution of helium bubbles, surface morphology, and property changes of tungsten exposed to low-energy helium plasma. The current gap and outstanding challenges to establish a predictive modeling capability for dynamic evolution of PFM are discussed.

Modelling of surface morphology and roughness in fluid jet polishing

Fluid jet polishing (FJP) has been extensively used in various kinds of fields such as precision molding, optical components, etc. However, previous works mainly focused on the material removal process on the macro-scale (e.g., tool influence function, surface generation) to improve the form accuracy, the understanding of surface morphology evolution of FJP on the micro-scale is still far from complete, which makes it difficult to predict the surface quality under certain polishing conditions. Time-consuming and high-cost trial and error are usually needed to obtain suitable polishing conditions for specific surface quality requirements. In this paper, a physical model was developed to predict the surface morphology and roughness after FJP, by combining the computational fluid dynamics (CFD) simulation and kinetic analysis of the abrasives. The single abrasive erosion process including indentation action, ploughing action, and cutting action was analyzed by kinetic analysis. Besides, the overlap of single abrasive erosion pits was modeled to simulate the surface morphology evolution in FJP and determine the surface roughness after polishing. Different parameters were considered in the model including jet pressure, jet angle, and abrasive size. A series of polishing experiments were conducted to validate this model and the effect of different polishing parameters on surface quality was elucidated by the impact velocity distribution and erosion morphologies. It is found that the simulation results agree well with the experimental results. This paper not only provides a deeper understanding of the microscale material removal in FJP, but also provides an effective method for the prediction of surface roughness in FJP.

Fabrication of micro-nano structure Se-doped silicon via picosecond laser irradiation assisted by dopant film

Se-doped silicon with micro-nano structures was designed and fabricated by irradiating Si-Se bilayer films coated crystalline silicon using picosecond laser pulses. In order to explore the evolution of surface morphology carried out by picosecond laser irradiation, four scanning speeds of 100 mm/s, 200 mm/s, 400 mm/s and 600 mm/s were tried in this study, respectively. The morphology test results show that the laser induces surface micron-scale grooves covered with nanoscale particles. EDS spectra demonstrates the presence of Selenium in the black silicon after an average of 400 pulses per unit area. The average reflectivity of the Se-doped silicon is as low as 3.45 % over the range of 1000–1700 nm when the scanning speed is 100 mm/s, and the corresponding Hall mobility is about 491 cm2 v−1 S−1. Furthermore, Raman spectra results indicate that picosecond laser irradiation does not destroy the crystalline phase, which is of great importance for the application of micro-nano structured Si in optoelectronic devices.

Heteroepitaxy of Large-Area, Monocrystalline Lead Halide Perovskite Films on Gallium Arsenide.

Lead halide perovskite materials have been emerging as promising candidates for high-performance optoelectronic devices. Significant efforts have sought to realize monocrystalline perovskite films on a large scale. Here, we epitaxially grow monocrystalline methylammonium lead tribromide (MAPbBr3) films on lattice-matched gallium arsenide (GaAs) substrates on a centimeter scale. In particular, a solution-processed lead(II) sulfide (PbS) layer provides a lattice-matched and chemical protective interface for the solid-gas reaction to form MAPbBr3 films on GaAs. Structure characterizations identify the crystal orientations in the trilayer MAPbBr3/PbS/GaAs epistructure and confirm the monocrystalline nature of MAPbBr3 on PbS/GaAs. The dynamic evolution of surface morphologies during the growth indicates a two-step epitaxial process. These fundamental understandings and practical growth techniques offer a viable guideline to approach high-quality perovskite films for previously inaccessible applications.

Cavitation-Erosion behavior of laser cladded Low-Carbon Cobalt-Based alloys on 17-4PH stainless steel

Stellite 728 (C14) with low-carbon and high-molybdenum was used for cavitation resistance application in this research. The specimens were fabricated on the surface of a martensitic precipitation hardening stainless steel called 17-4PH by laser cladding technique. The cavitation erosion behavior in 3.5 wt% NaCl solution is investigated using a 20 kHz vibratory cavitation erosion test machine. The electrochemical corrosion test was also explored to reveal the mechanism of the synergistic effect of cavitation and electrochemical corrosion. The experimental results of the Stellite 728 were compared with those of well-known cavitation-resistant Stellite 6 and wrought Stellite 6B. The surface morphology and microstructure evolution after cavitation were analyzed by means of metallographic microscope (OM), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and 3D optical surface morphometry to explore the cavitation erosion mechanism of the specimens. The experimental results show that the Co-based alloys have better cavitation erosion resistance than 17-4PH, and laser cladded Stellite 728 has better cavitation resistance in 3.5 wt% NaCl solution than laser cladded Stellite 6 and wrought Stellite 6B, owing to the formation of large amounts of Mo-rich intermetallic compound in the alloy.

Surface morphology and deuterium retention in W and W-HfC alloy exposed to high flux D plasma irradiation

In this work, pure W and W-0.5wt%HfC alloy (WHC05) were fabricated by sintering and hot-rolling following the same processing route. After exposing to a high flux deuterium plasma irradiation with the D+ flux to three fluences of 6.00 × 1024, 2.70 × 1025 and 7.02 × 1025 D/m2, the evolution of surface morphology, deuterium retention and hardening behaviors in pure W and WHC05 has been studied. The SEM results show the formation of D blisters on the irradiated area, and with the increase of D implantation, the size of these blisters increases from 200 ∼ 500 nm (2.70 × 1025 D/m2) to 1 ∼ 2 μm (7.02 × 1025 D/m2) in WHC05 and from 1 ∼ 2 μm (2.70 × 1025 D/m2) to > 3 μm (7.02 × 1025 D/m2) in pure W, respectively. A higher D retention and obvious hardening are observed in pure W than that of the WHC05 alloy, indicating an improve radiation resistance in WHC05 compared to pure W.

Helium-induced morphology evolution in tungsten under thermal treatment

Surface and near-surface morphology evolution of helium-irradiated tungsten due to thermal cycling up to the ITER-relevant temperature of 1350 K was studied using electron microscopy and positron annihilation spectroscopy techniques. Holes at the surface and bubbles in the near-surface of recrystallized polycrystalline tungsten samples were created by 75 eV helium plasma irradiation with the fluence of 3 × 1023 He m−2 at the surface temperature of 1073 K. Subsequent annealing experiments were combined with a detailed electron microscopy analysis to investigate the shape and density changes of holes and helium bubbles with respect to grain orientation. We show that the initially circular holes and round bubbles became faceted upon heating with 1 K s−1 ramp up to 870 K. Annealing cycles up to 1350 K induced resulted in bubbles removal in the first 5 nm below the surface and surface smoothing. Electron energy loss spectroscopy measurements allowed estimation of helium gas density and pressure inside bubbles. Positron annihilation spectroscopy allowed to investigate the nature of defects and their evolution in the helium-irradiated tungsten with thermal cycling.

Surface morphological and optical evolution of RF sputtered AZO films for optoelectronic devices

Herein, aluminium-doped zinc oxide (AZO) films were fabricated onto borosilicate glass and fluorine-doped tin oxide (FTO) substrates by RF sputtering. Surface morphology and scaling studies of these films revealed the formation of large grain in AZO films fabricated onto the glass substrates. Several fractal parameters of all samples have been evaluated to understand the deeper morphological insights of observed surfaces. Optical investigations revealed a higher transmittance of ∼93% in the visible region for FTO/AZO films. Estimated values of Urbach energy are found to be 0.20 eV and 0.17 eV for glass/AZO and FTO/AZO films, respectively. Important optical constants such as refractive indices, extinction coefficients, etc have been investigated to explore the optical mechanism of these films. Furthermore, photoluminescence studies suggest the reduction in the deep-level emission defect states for AZO films fabricated onto FTO substrate. These results propose that AZO films may be suitable for use in optoelectronics.

Influence of surface temperature, ion impact energy, and bulk tungsten content on the sputtering of steels: In situ observations from plasma exposure in PSI-2

• PSI-2 deuterium plasma exposures of 3 RAFM steels. • In-situ measurement of relative sputtering yields by optical emission spectroscopy. • In-situ measurement of the evolution of surface morphology by IR camera. • Post-mortem measurement of tungsten enrichment by RBS, SEM and EDX. • Independent measurements allow to disentangle the impact on the erosion of Fe. This study presents results from PSI-2 deuterium plasma exposures of reduced-activation ferritic martensitic steels with different tungsten content at a peak plasma flux of 9 · 10 20 D/m 2 s and 420–920 K sample temperature. Via optical emission spectroscopy the relative sputtering yield of Fe and Cr, and via an infrared camera the evolution of surface morphology is studied in-situ in 2D. After the exposure, RBS, SEM and EDX reveal tungsten enrichment and the formation of surface structures. Due to the independent measurement of surface morphology and tungsten enrichment, it is possible to disentangle the impact of both effects on the erosion of Fe. As part of this study, we investigate the effects of tungsten content, sample temperature and ion impact energy. The results show a reduction of the sputtering yield, depending on the exposure conditions, up to a factor of 2 at 130 eV ion impact energy and 720 K sample temperature.

On the Classical Solutions for the Kuramoto-Sivashinsky Equation with Ehrilch-Schwoebel Effects

The Kuramoto-Sivashinsky equation with Ehrilch-Schwoebel effects models the evolution of surface morphology during Molecular Beam Epitaxy growth, provoked by an interplay between deposition of atoms onto the surface and the relaxation of the surface profile through surface diffusion. It consists of a nonlinear fourth order partial differential equation. Using energy methods we prove the well-posedness (i.e., existence, uniqueness and stability with respect to the initial data) of the classical solutions for the Cauchy problem, associated with this equation.

Surface Roughening Behavior of the 6063-T4 Aluminum Alloy during Quasi-in Situ Uniaxial Stretching.

Owing to orange-peel defects, the industrial application of light alloy structural members is significantly restricted. In this study, a quasi-in situ axial tensile experiment was conducted on a 6063-T4 aluminum alloy sample. The surface morphology and microstructure evolution of the tagged area were scanned simultaneously using laser scanning confocal microscopy and electron backscattered diffraction, and the surface roughening behavior of the polycrystal aluminum alloy surface, caused by deformation, was quantitatively analyzed. As the concave–convex features at the surface appear in pairs with increasing global strain, the width of the concave features increases, whereas that of the convex features decreases gradually, resulting in the initially increasing surface roughness, which subsequently remains unchanged. During the stretching process, the small-sized grains in the 37~102 μm range show weak strain localization and the highest coordination of deformation. The deformation mode of medium-sized grains in the 114–270 μm range tends to grain deflection, and others tend to slip.

Elaboration and characterization of porous ultrathin gold films grown by ion beam assisted deposition

The growth of ultrathin gold layers on a silicon substrate is performed with an unconventional ion beam assisted deposition. In this setup, evaporated gold flow and ion beam flux are perpendicular. 5 and 10 nm thick gold were deposited on tilted samples with the assistance of an argon ion beam at energies of 70 and 150 eV. We explored the evolution of surface morphology, mainly roughness and porosity, with ion bombardment for two gold thicknesses. We have also extrapolated Young’s modulus of these ultrathin layers by means of high-frequency acoustic measurements in the 90–260 MHz range. We also investigated the evolution of wettability of our structures with ion bombardment as well as their electrical and optical responses.

Pit rim decomposition into multiple quantum dots on surfaces of epitaxial thin films grown on pit-patterned substrates

We report results of dynamical simulations according to an experimentally validated surface morphological evolution model on the formation of regular arrays of quantum dot molecules (QDMs) consisting of 1D arrays of smaller interacting quantum dots (QDs). These QD arrays form along the sides of each pit rim on the surface of a coherently strained thin film epitaxially deposited on a semiconductor substrate, the surface of which consists of a periodic pattern of inverted prismatic pits with rectangular pit openings. We find that this complex QDM pattern results from the decomposition of the pit rim from a “quantum fortress” with four elongated QDs into four 1D arrays of multiple smaller QDs arranged along each side of the pit rim. Systematic parametric analysis indicates that varying the pit opening dimensions and the pit wall inclination directly impacts the number of QDs in the resulting QDM pattern, while varying the pit depth only affects the dimensions of the QDs in the nanostructure pattern. Therefore, the number, arrangement, and sizes of QDs in the resulting pattern of QDMs on the film surface can be engineered precisely by proper tuning of the pit design parameters. Our simulation results are supported by predictions of morphological stability analysis, which explains the pit rim decomposition into multiple QDs as the outcome of a tip-splitting instability and provides a fundamental characterization of the post-instability nanostructure pattern. Our theoretical findings can play a vital role in designing optimal semiconductor surface patterns toward enabling future nanofabrication technologies.

Surface morphology evolution behavior and SERS performance of Mo-Ag-Cu-Co films

Mo-Ag-Cu-Co films were fabricated by co-sputtering Ag/Mo and Co/Cu composite targets. Results show that a large number of particles grew on the surface of Mo-Ag-Cu-Co films before and after annealing. The number, size and components of these self-grown particles could be adjusted and controlled by changing annealing temperatures. The differences in diffusion of Ag, Cu, Co and Mo in Mo-Ag-Cu-Co films is the major mechanism of forming nanoparticles with different components. As the annealing temperature was lower than 260 °C, the self-formed particles were Ag single-crystal particles due to the stronger diffusion ability of Ag at low annealing temperatures. The stronger diffusion ability of Cu promotes the formation of AgCu particles after annealing at higher temperatures. However, the number of Ag atoms is much more than that of Cu atoms, which results in the presence of Ag particles. It was the first time that the monodispersed Ag particles and Ag-Cu particles were obtained on alloy films by magnetron sputtering without any template. These alloy films as SERS substrates presented excellent SERS performance and detected the characteristic Raman spectrum of 5 × 10−12 mol/L rhodamine 6g (R6G) solution, which could be ascribed to the enhanced electromagnetic field among heterogeneous particles.

Surface Morphology Evolution during Chemical Mechanical Polishing Based on Microscale Material Removal Modeling for Monocrystalline Silicon.

Chemical–mechanical polishing (CMP) is widely adopted as a key bridge between fine rotation grinding and ion beam figuring in super-smooth monocrystalline silicon mirror manufacturing. However, controlling mid- to short-spatial-period errors during CMP is a challenge owing to the complex chemical–mechanical material removal process during surface morphology formation. In this study, the nature of chemical and mechanical material removal during CMP is theoretically studied based on a three-system elastic–plastic model and wet chemical etching behavior. The effect of the applied load, material properties, abrasive size distribution, and chemical reaction rate on the polishing surface morphology is evaluated. A microscale material removal model is established to numerically predict the silicon surface morphology and to explain the surface roughness evolution and the source of nanoscale intrinsic polishing scratches. The simulated surface morphology is consistent with the experimental results obtained by using the same polishing parameters tested by employing profilometry and atomic force microscopy. The PSD curve for both simulated surface and experimental results by profilometry and atomic force microscopy follows linear relation with double-logarithmic coordinates. This model can be used to adjust the polishing parameters for surface quality optimization, which facilitates CMP manufacturing.